Blocks & Environment Business

Development of Resilient Breakwaterby Protecting Harbor-Side rubble foundation

The 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami destroyed many breakwaters. One cause was unexpected: the scouring of the rubble mound and subsoil by tsunami overflow. There is thus a need for a resilient structure for breakwaters that cannot be destroyed so easily.
Raising the mound height on the harbor side with widening stones can be regarded as effective in boosting the strength and resistance of the breakwater. However, depending on overflow conditions, armor stones cannot protect the rubble mound. We have therefore proposed a technology to make breakwaters resilient to against tsunami overflow by protecting the rubble foundation with highly stable wave dissipating blocks and armor blocks. The required mass of the blocks is calculated by a method devised by Fudo Tetra that has been appraised as simple and highly accurate. This technology was included in ‘Tsunami-Resistant Design Guideline for Breakwaters’ published by the Ministry of Land, Infrastructure, Transport & Tourism (December 2015, partly revised) and in the ‘Manual for Calculating Required Mass of Armor Blocks for Widening Works of Breakwater to Protect against Tsunami Overflows’ published by the Association for Innovative Technology on Fishing Ports and Grounds. It is in use in actual designs for resilient breakwaters around ports and fishing harbors. Furthermore, we are continuing to develop more sophisticated technologies for tsunami protection using advanced tsunami-generating equipment (chamber-type tsunami generator) that can accurately recreate tsunami wave patterns that occur in the ocean.

Technology to Maintain harbor calmness against Long-Period Waves

In many ports and harbors, it has been reported that long-period waves (wave periods from several seconds to several minutes) cause trouble in cargo handling. One way to resolve this is to build mound structures on the harbor side of breakwaters. Conventionally, a structure of rubble stones that projects above sea level has been used, but as this method extends width, a smaller-sized structure is desirable from the viewpoint of cost and suitability for confined harbor space.
　As a solution, we have proposed a new submerged structure to absorb long-period waves. The crown of this compact structure is level with the still water level. The width of the structure can be calculated using a table formulated from the results of hydraulic model tests, and this has been utilized in actual design.

Application of Numerical Wave Flume to Evaluating the Performance of Maritime and Coastal Structures

Working for Coral Reef Restoration

In recent years, there have been growing demands in society for the maximum possible conservation of the natural landscape and ecology often lost through the construction of marine structures such as breakwaters and seawalls. The destruction of natural coral reefs found all along the coast resulting from the development of coastal defenses has also become a social issue.
In 1998 an unusual increase is seawater temperature was experienced worldwide, and natural coral reefs in various locations were greatly damaged by coral bleaching, affecting the fishing industry and tourism. In particular, the main Okinawan island suffered devastating damage, and because sources of coral larvae are very limited, the restoration of coral reefs is expected to take considerable time.
With the aim of conserving and reestablishing precious coral reefs, Fudo Tetra is working on methods for the restitution of reefs lost through marine construction work and the rapid regeneration of coral damaged by bleaching. These include developing technologies for transplanting coral by the release of large quantities of coral larvae from artificial nursery production using gamogenesis, and for the large scale relocating of vulnerable coral reefs to more beneficial environments where there is far less influence from construction work.
To make this transplanting and relocating of coral reefs more reliable, we are developing a technique to quantify the environmental conditions at locations where healthy coral reefs have developed in order to select appropriate locations for coral transplanting.